Metal bending with an anti-galling bend fixture

ABSTRACT

A bend fixture for bending metal sheet includes a stationary platen, a hinged platen, and a hinge associated with the hinged platen. Each platen includes an exterior surface portion for supporting a metal sheet; an interior surface portion spaced from the exterior surface portion; and a slanted surface portion between the interior and exterior surface portion. The exterior surface portions of the platens are initially separated by a gap. Rotating the hinged platen about the hinge narrows the gap and causes the slanted surface portions to approach each other. A clamp above each platen supports the metal sheet adjacent the platens as the hinged platen is rotated. Bending metal sheet with the claimed bend fixture avoids surface galling associated with prior art sheet bending techniques relying upon interaction between a punch and a die.

1. FIELD OF THE INVENTION

The present invention relates to the bending of metal sheet and more particularly to a method and apparatus for bending metal sheet without detrimentally affecting surface quality in a bending zone.

2. BACKGROUND OF THE INVENTION

Techniques are known in the prior art for imparting to metal sheet a substantial angular bend, for example a 90° bend. Prior art methods for bending metal sheet at a 90° angle usually require positioning the metal sheet between a punch or punch tool and a die. However, interaction between the punch and the die galls the metal in a bend zone adjacent a bend line where the metal sheet is shaped so that visible streaks appear on the metal surface. Interaction between the punch and the die also risks metal excess or metal deficiency in the bending zone. Accordingly there still remains an unmet need for a bend fixture and method capable of bending metal sheet without detrimentally affecting metal surface quality in the bending zone.

A principal objective of the present invention is to provide a method and a bend fixture for bending metal sheet without galling surfaces of the metal sheet.

A related objective of the invention is to provide a method and a bend fixture for bending metal sheet without positioning the sheet between a punch and a die.

An advantage of the invention is that the claimed method and apparatus are capable of being automated for efficient large volume production of bent metal sheet. Additional objectives and advantages of my invention will become readily apparent to persons skilled in the art from the following detailed description of a particularly preferred embodiment.

3. SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a bend fixture including a first platen, a second platen, at least one hinge connected with at least one of the platens, and a clamp or clamping means for holding a metal sheet adjacent exterior surface portions of the first and second platens. Preferably the first platen is stationary and the second platen is connected with at least one hinge. The hinge preferably includes hinge pins attached to opposite lateral sides of the hinged platen. The stationary platen and the hinged platen are initially separated by a gap.

The stationary platen and the hinged platen each include an exterior surface portion, an interior surface portion spaced from the exterior surface portion, and a slanted surface portion extending angularly between an inner edge of the exterior surface portion adjacent to the gap and an inner edge of the interior surface portion spaced from the gap. The inner edge of the interior surface portion is spaced longitudinally outwardly of the inner edge of the exterior surface portion. The exterior surface portion preferably includes a generally planar principal portion spaced longitudinally from the gap and a convexly curved end portion between the principal portion and the gap.

The metal sheet to be bent in accordance with my invention may be made of a zirconium alloy, steel, aluminum, or copper. In a particularly preferred embodiment the metal bending apparatus and method are utilized for applying a 90° bend to a Zircalloy perimeter grid strap making up a part of a lattice for supporting nuclear reactor fuel elements. The perimeter grid straps interlock with ends of inner grid straps to form a lattice, as described in greater detail in Richards U.S. Pat. No. 5,859,887, the disclosure of which is incorporated herein by reference to the extent consistent with the present invention. Zirconium alloy sheet is particularly preferred because of its low neutron absorption cross-section. As used herein the term “sheet” refers to metal having a thickness of about 0.006 inch to 0.060 inch.

In the metal bending method of the invention a metal sheet is supported adjacent the planar principal portions of the first and second platens, spanning the gap between the platens. A first clamp holds the metal sheet to the first platen and a second clamp holds the metal sheet to the second platen. The first platen is preferably stationary while the second platen is preferably rotated on its hinge, preferably to an angle of greater than 90°. The hinged platen is preferably rotated by an angle of about 2.5° greater than the desired bend angle in order to overcome metal stress. Rotating the hinged platen bends the metal sheet, preferably to an angle of about 90°. When the hinged plate is rotated to the desired angle, the slanted portions of the stationary and hinged platens approach each other and portions of the metal sheet adjacent the gap approach the curved end portions of the platens in a bend zone extending transversely across the sheet. A bend line extending across the entire width of the metal sheet in the bend zone is remarkably free of streaks and other visible defects resulting from galling.

In a preferred embodiment of the invention wherein the metal sheet includes laterally outwardly extending vanes or tabs, the stationary platen and the hinged platen each include at least one exteriorly extending pilot pin positioned adjacent the vanes. The pilot pins stabilize the metal sheet as it is bent.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first side elevational view of a bend fixture of the invention.

FIG. 2 is a second side elevational view of a bend fixture of the invention.

FIG. 3 is a top plan view of a bend fixture of FIG. 1.

FIG. 4 is an end view of the bend fixture of FIG. 1.

FIG. 5 is an enlarged fragmentary cross-sectional view of the hinge pin area of FIGS. 1-4.

FIG. 6 is a first schematic view of a bend fixture of the invention, showing a metal sheet before bending.

FIG. 7 is a second schematic view of a bend fixture of the invention, showing a bent metal sheet.

5. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A particularly preferred embodiment of a bend fixture 10 made in accordance with the invention is shown in FIGS. 1-5. Referring more particularly to FIGS. 1 and 3, the bend fixture 10 includes a stationary platen or first platen 12 and a second platen or hinged platen 14. The fixture 10 also includes a subplate 16 anchored to a work table 18 by several bolts 20. The stationary platen 12 is fixed to the subplate 16 by bolts 22. A skirt 24 extends downwardly from the subplate 16, below the stationary platen 12. A stop bolt or stop 26 extends through the skirt 24 and outwardly thereof. The stationary platen 12 is separated from the hinged platen 14 by a short gap 27, best shown in FIG. 5.

The hinged platen 14 is connected with hinges on opposite sides thereof. Each hinge includes a generally cylindrical hinge pin 30, two fixed hinge covers 32 attached to the stationary platen 12 (one on each side), and two movable hinge covers 34 attached to the hinged platen 14 (one on each side). The hinged platen includes a handle 36 comprising a socket head cap screw. A manual operator pushes downwardly on the handle 36 in order to rotate the hinged platen 14 between the initial position shown in FIG. 1 and the rotated position shown in FIG. 2.

Referring again to FIG. 1, the stationary platen 12 includes an exterior surface portion 38 and an interior surface portion 40 spaced from the exterior surface portion. The exterior surface portion 38 is parallel to the interior surface portion 40. As shown in FIGS. 1 and 5, the exterior surface portion 38 includes a generally planar principal portion 38 a spaced from the gap 27 and a convexly curved end portion 38 b extending between the principal portion 38 a and the gap 27. The stationary platen 12 also includes a slanted surface portion 42 extending angularly between an inner edge of the exterior surface portion 38 adjacent the gap 27 to an inner edge of the interior surface portion 40 spaced from the gap 27. Similarly the hinged platen 14 includes an exterior surface portion 48 and an interior surface portion 50 spaced from the exterior surface portion. The exterior surface portion 48 is parallel to the interior surface portion 50. The exterior surface portion 48 includes a generally planar principal portion 48 a spaced from the gap 27 and a convexly curved end portion 48 b extending between the principal portion 48 a and the gap 27. The hinged platen 14 also includes a slanted surface portion 52 extending angularly between an inner edge of the exterior surface portion 48 adjacent the gap 27 to an inner edge of the interior surface portion 50 spaced from the gap 27.

As shown in FIGS. 1-3, the bend fixture 10 includes a first clamp or clamping plate 54 supported above the stationary platen 12 by a support strut 56. The first clamp 54 includes a generally planar lower surface 57. The first clamp 54 is moved downwardly toward the stationary platen 12 by a piston activated by air from a pressure cylinder 58. A threaded screw 60 is rotated to fit into an upwardly extending screw hole 62 in the first clamp 54. Similarly, a second clamp 64 is supported above the hinged platen 14 by support strut 66. The second clamp 64 is moved downwardly toward the hinged platen 14 by air from a pressure cylinder 58. A threaded screw 60 is rotated to fit into an upwardly extending screw hole 62 in the second clamp 64. The second clamp 64 has a generally planar lower surface 67. The first clamp 54 and the second clamp 64 each define a shallow recess 68 extending upwardly from the respective lower surfaces 57, 67. In a particularly preferred embodiment wherein the bend fixture 10 is used to bend metal sheet having a thickness of about 0.025 inch, the recess 68 has a depth of about 0.023 inch. This depth is selected to reduce direct contact between clamp lower surfaces 57, 67 and their respective platens 12, 14.

As shown in FIGS. 1-3, the stationary platen 12 and the hinged platen 14 each define several downwardly extending indentations 70. The indentations are sized and shaped to accommodate structures projecting outwardly from the metal sheet. Such projections include dimples and springs when the metal sheet is a 0.025 inch thick Zircalloy sheet shaped for use as a perimeter grid strap in a lattice supporting nuclear fuel elements. The hinged platen 12 also includes upwardly extending pilot pins 75 for stabilizing the metal sheet by standing aside a vane in the sheet. The vane is preferably concavely shaped to fit the convex outer curvature of the pilot pin 75. The sheet is bent by rotating the hinged platen 12 from the initial position shown in FIG. 1 to the final position shown in FIG. 2. As shown in FIG. 2, such rotation causes the slanted portions 42, 52 of the platens 12, 14 to approach each other. The stop 26 is adjustable to vary the bend distance by rotating the stop 26 to a preselected position.

FIG. 5 is an enlarged, fragmentary view of a portion of the bend fixture in the vicinity of a hinge pin 30. The bend fixture 10 includes a stationary platen 12 spaced from a hinged platen 14 by a gap 27. The stationary platen 12 includes an exterior surface portion 38 and an interior surface portion (not shown) spaced from the exterior surface portion. The exterior surface portion 38 includes a generally planar principal portion 38 a spaced from the gap 27 and a convexly curved end portion 38 b extending between the principal portion 38 a and the gap 27. The stationary platen 12 also includes a slanted surface portion 42 extending angularly between an inner edge of the exterior surface portion 38 adjacent the gap 27 to an inner edge of the interior surface portion (not shown). Similarly the hinged platen 14 includes an exterior surface portion 48 and an interior surface portion (not shown) spaced from the exterior surface portion 48 and extending generally parallel thereto. The exterior surface portion 48 includes a generally planar principal portion 48 a spaced from the gap 27 and a convexly curved end portion 48 b extending between the principal portion 48 a and the gap 27. The hinged platen 14 also includes a slanted surface portion 52 extending angularly between an inner edge of the exterior surface portion 48 adjacent the gap 27 to the interior surface portion (not shown).

FIGS. 6 and 7 schematically illustrate a metal sheet 105 positioned adjacent a bend fixture 110 including a stationary platen 120 and a hinged platen 122. The platens 120, 122 are initially separated by a small gap 124. The platens each include an exterior surface portion 120 a, 122 a below the metal sheet 105, an interior surface portion 120 b, 122 b on a side opposite the exterior surface portions 120a, 122 a, and a slanted surface portion 120 c, 122 c extending angularly between the exterior surface portions 120 a, 122 a and the interior surface portions 120 b, 122 b adjacent the gap 124. Exterior surface portions 120 a, 122 a of the platens each include a generally planar principal portion 120 d, 122 d spaced from the gap 124 and a convexly curved end portion 120 e, 122 e between the respective principal surface portions 120 d, 122 d and inner edges 120 f, 122 f adjacent the gap 124. The metal sheet 105 to be bent on the fixture 110 is positioned by pilot pins (not shown) extending outwardly of the platens 120, 122 and then clamped next to the platens 120, 122 by clamping plates (not shown).

Initially as shown in FIG. 6 the metal sheet 105 extends longitudinally across the gap 124, spaced upwardly of inner edges 120 f, 122 f of the platens 120, 122. The hinge covers associated with the hinged platen 122 are not shown in FIGS. 6 and 7 although the location of the center or centerline 130 of the hinge pin is shown. Precise location of the centerline 130 is important in bending a metal sheet 105 in the bend fixture 110. Fortunately, the centerline 130 can be located precisely by following the following equation: $C = \frac{0.017453 \times {D\left( {R + {{.333} \times T}} \right)}}{2}$ where D is the angle of bend in degrees, R is the inside radius of the bend in inches, T is the thickness of the metal sheet in inches, 0.017543 radians/degree is the factor for converting degrees to radians, and C is the horizontal and vertical distance from the centerline 130 to the center 135 of the inside radius of the bend 140 in the sheet 105.

In a preferred example where the bend angle is 90°, the sheet thickness is 0.026 in, and the bend radius is 0.100 in, the centerline distance, C, is calculated as follows: $\begin{matrix} {C = \frac{0.017453\quad{radians}\text{/}{degree} \times 90{^\circ}\quad\left( {{0.100\quad{in}} + {{.333} \times {.026}\quad{in}}} \right)}{2}} \\ {C = \frac{0.017453\quad{radians}\text{/}{degree} \times 90{^\circ}\quad\left( {{0.100\quad{in}} + {{.00866}\quad{in}}} \right)}{2}} \\ {C = {0.08534\quad{in}}} \end{matrix}$

In order to bend the metal sheet 105 to a desired angle it is necessary to overbend by about 2.5°, thereby overcoming internal metal stresses. An angular relief 140 of about 2.5° is shown in FIG. 6. As shown in FIG. 7, after the hinged platen 122 is rotated clockwise by about 92.5° so that its slanted surface portion 122 c approaches the slanted surface portion 120 c of the stationary platen 120, the sheet 105 attains a permanent bend angle of about 90°.

The foregoing detailed description of my invention has been provided with reference to a particularly preferred embodiment. Persons skilled in the art understand that numerous modifications can be made in my invention without significantly departing from the spirit and scope of the following claims. 

1. A method for bending a metal sheet comprising: (a) providing a bend fixture comprising a first platen and a second platen separated from the first platen by a gap, at least one of said platens being connected with at least one hinge, said first platen and said second platen each having an exterior surface portion, an interior surface portion spaced from the exterior surface portion, and a slanted surface portion extending angularly between an inner edge of the exterior surface portion adjacent said gap and an inner edge of the interior surface portion spaced from said gap, said exterior surface portion including a generally planar principal portion spaced from the gap and a convexly curved end portion between the principal portion and the inner edge of the exterior surface portion, (b) supporting a metal sheet adjacent said principal portions of the first and second platens, said metal sheet being spaced exteriorly of the inner edges of the exterior surface portions of the first and second platens, and (c) rotating at least one of said first and second platens about said hinge while retaining said metal sheet adjacent exterior surface portions of the first and second platens so that said slanted portions of the first and second platens approach each other, portions of the metal sheet adjacent the gap approach the curved end portions of the platens, and said metal sheet bends in a bend zone extending transversely across said sheet adjacent said curved end portions.
 2. The method of claim 1 wherein step (b) includes clamping said metal sheet to said principal portion of the first platen with a first clamp and clamping said metal sheet to said principal portion of the second platen with a second clamp spaced from said first clamp.
 3. The method of claim 1 wherein said metal sheet includes at least one vane extending laterally outwardly and step (b) includes positioning at least one pilot pin adjacent said vane.
 4. The method of claim 1 wherein said principal portions of the first and second platens are generally coplanar.
 5. The method of claim 1 wherein the first platen is stationary and the second platen is hinged.
 6. The method of claim 5 wherein the second platen is connected with hinge pins located on opposite lateral sides of the second platen.
 7. The method of claim 1 wherein said exterior surface portions of the first and second platens are generally parallel to the interior surface portions.
 8. The method of claim 1 wherein said bend zone extends linearly across an entire width of said metal sheet.
 9. The method of claim 1 wherein step (c) includes bending said metal sheet at an angle of about 90°.
 10. The method of claim 1 wherein in step (c) said slanted portions of the first and second platens approach each other.
 11. The method of claim 1 wherein said metal sheet comprises a metal selected from the group consisting of zirconium alloys, steel, aluminum alloys, and copper alloys.
 12. The method of claim 1 wherein said metal sheet comprises a zirconium alloy.
 13. A method for bending a metal sheet comprising: (a) providing a bend fixture comprising a stationary platen and a hinged platen separated from the stationary platen by a gap, said hinged platen including hinges on opposite lateral sides thereof, said stationary platen and said hinged platen each having an exterior surface portion and an interior surface portion spaced from the exterior surface portion, said exterior surface portion including a generally planar principal portion spaced from the gap and a convexly curved end portion between the principal portion and an inner edge of the exterior surface portion adjacent said gap, (b) clamping a metal sheet to the stationary platen with a first clamp and clamping said metal sheet to the hinged platen with a second clamp spaced from said first clamp, and (c) rotating said hinged platen about said hinges while retaining said metal sheet adjacent exterior surface portions of the first and second platens so that said metal sheet bends in a bend zone extending transversely across said sheet.
 14. The method of claim 13 wherein said metal sheet bends at an angle of about 90°.
 15. A bend fixture for bending metal sheet, comprising: (a) a stationary platen, (b) a hinged platen separated longitudinally from the stationary platen by a gap, said stationary platen and said hinged platen each including an exterior surface portion for supporting a metal sheet, an interior surface portion spaced from the exterior surface portion, and a slanted surface portion extending angularly between an inner edge of the exterior surface portion adjacent said gap and an inner edge of the interior surface portion, each said exterior surface portion including a generally planar principal portion spaced longitudinally from the gap and a convexly curved end portion between the principal portion and an inner edge adjacent the gap, (c) at least one hinge attached to the hinged platen, and (d) a first clamp for holding a metal sheet adjacent said exterior surface portion of the stationary platen and a second clamp for holding the metal sheet adjacent said exterior surface portion of the hinged platen when the hinged platen is rotated about the hinge to bend the metal sheet.
 16. The bend fixture of claim 15 wherein the inner edge of the interior surface portion of each said platen is spaced longitudinally from the gap.
 17. The bend fixture of claim 15 further comprising at least one pilot pin extending exteriorly of the stationary platen, said pilot pin stabilizing the metal sheet adjacent the stationary platen.
 18. The bend fixture of claim 15 wherein the first clamp includes a surface extending generally parallel to the principal portion of the stationary platen and the second clamp includes a surface extending generally parallel to the principal portion of the hinged platen.
 19. The bend fixture of claim 15 wherein the first clamp is spaced from the second clamp. 